Processes for sterilization of contact lenses are well known in the prior art. Typically such processes employ aqueous solutions of sterilants such as H.sub.2 O.sub.2 present in a concentration of 1-5 wt. %, together with adjuvants such as chelating agents (e.g. ethylenediaminetetraacetic acid), buffering agents such as alkali metal phosphates, alkali metal borates, alkali metal carbonates and mixtures thereof, etc.
After a contact time sufficient to disinfect the lens, the residual sterilant must be neutralized, i.e. converted into ophthalmologically innocuous by-products, since even traces of the sterilant remaining on the lens will result in irritation to the eye and concomitant discomfort to the contact lens wearer.
The most common method for neutralizing H.sub.2 O.sub.2 involves the use of a thin film of platinum on a plastic substrate, as disclosed in U.S. Pat. No. 3,912,451. Such prior art process suffers from several disadvantages. Firstly, this process is quite expensive, owing to the use of platinum. Of course, the device may be reused a number of times (up to a maximum of .about.100 times), but frequently the user continues to use the device well after the recommended maximum number of times, either because of inadvertence or to try to achieve further cost savings. Moreover, the decomposition rate of the H.sub.2 O.sub.2 is non-reproducible and will gradually diminish, thus affording a lack of certainty as to the continued effectiveness of the device. Finally, there is also the need to dispose of an envirormentally unfriendly material, i.e. platinum coated on a plastic substrate, since the device is not readily recyclable.
The prior art also teaches that chemical reducing agents, e.g. sodium thiosulfate, may be used to neutralize the residual H.sub.2 O.sub.2, see A. R. Gasset et al., Arch. Ophthalmol., vol. 93, June, 1975, pp. 412-415. It is also known to utilize a controlled-release sterilant system utilizing sodium percarbonate, see U.S. Pat. No. 4,863,627. However, such techniques are disadvantageous in that they introduce foreign substances which cause a change in the osmotic pressure of the ophthalmological solution and also a severe burning sensation in the eye or even irritation to the ocular tissue may result.
It is also known to use aqueous solutions of inorganic hypochlorites, i.e. alkali and alkaline metal hypochlorites as the sterilants for contact lenses together with reducing agents to neutralize the residual hypochlorite, see U.S. Pat. Nos. 3,717,580 and 4,167,561, Canadian Patent 1,087,955 and U.K. Patent 2,094,922.
U.S. Pat. No. 4,976,921 extends the concept of hypochlorite sterilants to compounds which are hypochlorite precursors, e.g. Chloramine-B, Chloraraine-T, Dichloramine-T, Halazone, chlorinated cyanuric acid, etc. It is taught that various reducing agents may be used to neutralize the residual hypochlorite precursors, e.g. sodium thiosulfate, .alpha.- and .beta.-hydroxy-carboxylic acids such as glycolic, malic, citric, lactic, tartaric, ascorbic, etc.
In many of the systems which employ slow-release inorganic hypochlorite or hypochlorite precursor compounds, a continuous loss of hypochlorite occurs which then entails higher concentrations of hypochlorite than otherwise needed. Such a situation may readily result in misuse by the consumer. Moreover, animal studies have shown that the use of hydroxy-carboxylic acids in the reduction of hypochlorites indicate that the reaction between these reactants produce physiologically irritating and perhaps toxic oxidation by-products, thereby limiting the usefulness of this method. In addition, all presently known methods of reducing hypochlorites bring about a concurrent change in the tonicity of the resulting aqueous solution, thereby causing discomfort to the contact lens wearer.